Plastic extrusion molding machine



Feb. 27, 1940. w. ERNST Er AL PLASTIC EXTRUSION MOLDING MACHINE Filed April 26, 1937 6 Sheets-Sheet 1 Feb. 27, 1940. w. ERNST Er AL 2,191,882

PLASTIC EXTRUSION MOLDING MACHINE Filed April 26, 1957 6 Sheets-Sheet 2 /A/VENTORS WALTER ERA/5T /fM E. LAWYER A TTU/P/VEYS Filed April 26, 1937 6 Sheets-Sheet 3 /NVE/V TCI/FS WAL TER ERNST /PA B. LA wwf/P A TTORNE YS Feb. 27, 1940. w. ERNST Er AL PLASTIC EXTRUSION MOLDING MACHINE Filed April 26, 1957 6 Sheets-Sheet 4 wkwww WALTER ERNST IRA B. LAWYER 4 TTOPNEYS Feb. 27, 1940.

' w. ERNST ET Al. PLASTIC EXTRUSION MOLDING MACHINE Filed April `26, 1937 6 Sheets-Sheet 5 v, Y v fs. m v f j s T R Y. Q MA@ v Q www v NE A. M v A O/,N /7/7 lff/l E R/W T w /A m Wm ,Feb` 27, '1940.4 w. ERNST Er AL 2,191,882

PLASTIC EX'TRUsIoN MOLDING MAcHI-NE Filed April 26, 1937 6 Sheets-.Sheet 6 /Nl/EA/ T0 RS WALTER ERNST y /RA B. LA WYE'R (Luba/vm@ Patented Feb. 27, 1940 UNITED STATES PLASTIC Ex'raUs'roN Ira B.

hio, assignors to The Hydrauli rp n, Del., a corporation of Dela- Application April 26, 1937, Serial No.

10 Claims.

but with a high Another object molding machine without the cushioning plungers.

Another object is to provide a plastic extrusion molding machine having positively actuated force feeding the plastic material into the injector.

Another object is to provide a. plastic extrusion molding machine, wherein the positive feedthe injector.

Another object is to provide a feeding mechanism for a plastic extrusion molding machine, this mechanism employing a feeding screw actuated by gearing from a motor unit in such a manner of the machine shown PATENTA IMomma mom Lawyer, Mount Gilead. c Press ik oFFicE 138,904 (Cl. y18-30) that the motor unit may be readily detached from the feeding screw so as to enable the easy cleaning of the feeding screw.

Another object is to provide a feeding mechadescribed in the preceding paragraph,

wherein a shear pin is provided 16 In the drawings: Figure 1` is a through the plastic extrusion molding machine 2o the left-hand I-l in Figure v2, along the line 5 5 in Figure 3.

Figure2 is a partial left-hand end elevation of the machine shown in Figure 1.

Figure 3 is a partial right-hand end elevation in Figure l.

Figure 4 is an enlarged substantially horizontal section of the left-hand end o1' Figure i, taken along the line M in Figure 2. o

Figure 5 is an enlarged substantially horizontal section taken along the Figure 6` is a vertical section along 6 8 in Figure 3, showing the feeding mechanism for the injection material.

Figure 7 is a cross section through the main and booster plungers, taken along the line 1-1 in Figure 4.

Figure 8 is a cross section through the forward end oi' the injection or extrusion chamber, taken y along the line 8`8 in Figure 6.

Figure 9 is feeding mechanism.

General arrangement In general, the plastic extrusion machine of this invention consists of a pair of dies, one 55 ing threaded sockets of which is moved by a plurality of hydraulic plungers into plunger providing a booster or rapid traverse speed and the other providing a slower or nfore powerful clamping effect. The other die is mounted upon cushioning plungers which are separable from cushioning pistons, the latter not being engaged until the plungers have moved back a predetermined distance. A hydraulic circuit is arranged to control these various hydraulic elements (shown in Figure l). The feeding and injecting mechanism shown in Figure 6, and on a smaller scale in Figure 1, consists of a heated injection chamber having a power-operated feeding screw for feeding the granular plastic material into the injector. The feeding screw is operated by a motor which is timed by a timing device, the latter in turn being controlled by the actuation of limit switches operated in re v sponse to the reciprocation of the injection plunger.

Molding machine construction The molding machine portion is shown in Figure 1, in diagrammatic form, certain of the purely mechanical and frame elements being omitted for clearness of showing. The molding portion consists, in general, of strain rods |I| having cross members |2 and I3, flxedly mounted thereon from left to right. The strain rods I0 also serve to guide the die carrier I4 and die head I5 in their reciprocating motion, as hereinafter described in detail.

Mounted upon the cross member is ahydraulic cylinder |6 with an inwardly extending hollow plunger I1 mounted inthe outer end thereof, and secured thereto as by the nut I8. The hollow plunger I1 is provided with a bore I9. The cylinder |6 is provided with a bore 20, within which reciprocates a main plunger 2|, of double-acting form, and having an internal bore 22 therein. The bore 22 serves as a cylinder bore for receiving the hollow plunger I1, and communication therewith is established through the hollow bore I9 in the hollow plunger I1. The hollow plunger I1 cooperates with the internal bore 22 of the main plunger 2| to provide a rapid traverse action of the latter, after which the main plunger itself is actuated by fluid within the bore 20 of the main cylinder I6.

On the right-hand end of the main plunger 2| is mounted the die carrier |4, the latter hav- 23 for the reception of the threaded limit rods 24, having heads 25 on the opposite ends thereof. The limit rods 24 serve to engage the cross member and 'limit the stroke of the die carrier I4 andmain plunger 2| in the event that the dies are omitted and the machine started while in that condition. The cylinder bore 20, at its outer end, is provided with a packing 26, compressed by a gland 21 for preventing the escape of uid around the main plunger 2|.

Mounted on the die carrier |4 is a die support 28 carrying a die 29, which forms one-half of a die assembly, the other half consisting of the oppositely disposed die 30. The die support 28 is, provided with a channel 3| for receiving the knock-outbar 32, actuatedby the rods 33 connected to the ends thereof when these vrods engage the cross member on the return stroke of the main plunger 2|, after the completion of a molding operation. The pins 34 are mounted on the knock-out bar holes 35, into the die cavities 36 of the die 29,

engagement with the other, one.

(Figures l and 5),

32 and pass through the when the knock-out position is reached (Figure 4). Adjustable stops 31, mounted on the strain rods I0, serve to engage the die carrier I4 and prevent it and the main plunger 2| from traveling further to the left than is required to open the dies 29 and 30 and eject the molded article This arrangement saves time in opening and closing thedies 29 and 30. v The die 30 is mounted upon a die support 38 both being bored centrally to admit an injection tube 39 having an injection socket 40 at its right-hand end. The die support 38 is mounted upon the die head I5, which as previously stated, is `slidably mounted for guidance along the strain rods IIJ. The die head I5 is centrally provided with an aperture 4|, permitting the injection mechanism to approach and `engage the socket 4|). The die head is bored to receiv'e bolts 42, the threaded ends of which 49 engaging sockets 44 in the die head I5. The opposite ends completely separable therefrom. The separablepiston heads 52 reciprocate within cylinder bores 53 which .are coaxial with and substantially form enlargements of the cylinder bores 41. The outer ends of the cylinder bores 53 are closedrby an end plate 54 having ports 55 therein for the admission of pressure fluid to the cylinder bores 53. Similarly, the cylinder bores 41 are Yprovided with ports 56 for a similar purpose. The end plate 54 is provided with a central port 51, serving to admit pressure fluid to a central cylinder 58, within which a piston head'59 reciprocates. The piston head 59 is bored to receive a piston rod 60, secured thereto by the nut 6| threaded upon the right-hand end thereof. A port 62 serves for the admission and discharge of iiuid from the opposite end of the cylinder bore 58. Packings 63 and 64, closed by the gland 65, serve to prevent the escape of viiuid around the piston rod 60. y

On the piston rod 60 is mounted an annular cam 66 for actuating certain limit switches, hereinafter described. To the left of the cam 66 the piston rod 60 is reduced in diameter -to form anl I therearoun'd Beyond the member 14 the injector chamber 12 is threaded,'as at 15, to receive a nozzle 16 having a conical wall 11 and an outlet passage 18.` The nozzle 16 is also provided with a protuberance 19 of corresponding vconfiguration to the socket 40, and adapted to mate therewith when the die head I5 and die support 38 are moved into engagement there-- with.

cloggmg of the feeding mechanism, hereinafter described. The heat-insulating disc 81 cooperates with the cooling chamber 90 to transmission of heat from the anged portion 88 of the flanged portion 88.

Feeding mechanism The feeding and injection mechanisms are shown in enlarged detail in Figure 6. The sleeve 68 is provided with n aperture 93, the mouth of an friction bearings |03 and |04 and carries a bevel gear |05, meshing with a. similar bevel gear |06 upon the cross shaft |01 leading into the gear box |08 of the motor |09. The gears |05 and |06 are arranged within a casing ||0, mounted to the cross member I2. The bored plate ||2 serves to close the casing and surrounds the shaft |02, the escape 0f fluid being prevented by the packing ||3.

screw assembly without disturbing the motor.

Mounted upon a bracket ||4, secured to the lower portion of the cross member |2 (Figure 6),

is a sliding plate ||6a which may be moved to limit switch ||5, a second limit switch 6 being mounted upon the sliding plate ||6a. The limit switches and ||6 are provided with rollers ||1 and I8 for v,actuating and closing the switches when they are engaged by the cam 66. The switches ||5 and ||6 are of a normally open l tains iive stroke of the plunger.

as a Whole will be discussed after the description of the electrical system.

Electrical feed actuating system 'I'he feed-operating circuit (Figures 10 and 11) includes a. five-pole motor starting switch |20, a timing switch |2|,a two-pole magnetic conanism. The auxiliary contact assembly |30, with contacts |3| and e ve-pole motor starting switch |20 conswitch blades |35, to |39, inclusive, mounted upon an armature rod |40 adapted to be operated by the operating coil |4| when the latter is energized. The switch blade I 39 serves |4| after its The switch blades |36, serve to conduct electricity from the power lines |42, |43 and |44 to the feeding The two-pole respectively. The switch an' interlock switch for closing the holding cirroller ||8 (Figure 6), and closes the second limit switch I6. When this occurs (Figure 11), the operating coil |45 of the two-pole magnetic contactor becomes energized through the timL ing switch assembly |24 and from the line |43 to the line |44. With the closing of the magnetic contactor switch |22, the switch blade |41 thereof likewise closes, and completes a holding circuit for the operating coil |45, even when the limit switch ||6 is released by the return As the plunger returns to its retracted position, the cam 66 depresses The coil |4|, thus energized, causes the motor starting switch |20 to close so that its five switch blades interconnect their corresponding poles. The closing of the switch blade |35 serves to energize the timing motor |23 of the timing switch |2|, and causes it to begin its cycle of operations. The closing of the switch blades |36, |31 and |38 causes the feeding motor |09 to be energized from the power lines |42, |43 and |44. The closing of the iinal switch blade |38 operates a holding circuit to maintain the coil |4| in an energized condimagnetic contactor with a chamber tion, even when the limit switch is released.

After the electrical timing switch |2| has run its course for the predetermined time for which it has been set, the circuit is opened at the timing switch contacts |24 (Figure 11). This action deenergizes the operating coils |4| and |45 of the motor starting switch |20 and magnetic contactor switch |22, causing the switch blades of both switches to disengage their respective contacts and open the circuits controlled thereby. The consequent opening of the magnetic contactor switch blade |35 (Figure 11) deenergizes the timing motor |23 and resets the timing device for another cycle of operations. This cycle of operations is repeated when the injection plunger executes another working stroke and returns to its original position, thereby again actuating the limit switches ||5 and ||6.

Under these conditions the timing switch has been so adjusted that the motor will run for a sufficient length of time to inject into the chamber slightly more than the correct amount of material. This slight over-feeding prevents a scarcity of material and accordingly the injection plunger 61, after several strokes, is incapable of completing a working stroke on account of the piling up of material within the bore or chamber 10. When this happens the cam 66 does not move sufficiently far to the left to close the limit switch ||6 so that the circuit which energizes the magnetic contactor switch |22 is not completed. When starting position and the cam 66 closes the limit switch ||5, under such conditions no energization of the operating coils |4| and I45jtakes place, hence, the motor |09 fails to operate to actuate the feed screw 99. On the next stroke of the plunger 61 terial will be injected into the dies, thereby relieving the surplus quantity in the injection bore 10. The plunger 61 then travels sufficiently far to the left to close the limit switch ||6, and the complete cycle of operations is again carried out.

Hydraulic circuit The central bore |9 of the booster plunger |1 -is provided with an outlet port |50, from which runs to a die-clamping valve |52 (Figure 1). From the pipe |5| a branch |53 runs to a platen-operated valve |54, from which a return line |55 runs to the inlet port |56 of the main cylinder bore 20. The latter is also provided with a port |51, from which a line |58 runs to a check valve |59, a line |60 continuing therefrom to the oil reservoir or tank |6|. The die carrier |4 is provided with an arm I4, positioned to engage spaced collars |54b and |54 on opposite sides of the arm |4a and mounted upon the control rod |545 by which the valve |54 is shifted to its open and closed positions, respectively. The check valve |59 is provided |62 within which a pawl |63 engages a seat |64 to permit the flow of uid solely in the direction of the reservoir |6| to the main cylinder bore 20. From the line |5| a branch line |65 runs to a leakage pump |66, the suction line |61 therefrom running to the From the piston valve |52 the pressure line |68 runs to the main pump |69, the suction line |10 running therefrom to the tank |6|. The pressure line |68 contains a check valve I1| for permitting the flow of fluid solely in the direction from the pump |69 to the valve |52, and

the plunger returns to .its

the excessive quantity of madirection. From the valve |52 the line |12 runs to a port |13 leading into `the opposite end of the main cylinder 20 from the port |56. A branch line |14 with a manually operated valve |15 runs from the line |12 to the port 56 in the cylinder bores 41, thereby admitting and discharging fluid from the space to the left of the pistons 52. Similarly, a line |16 runs from the line |68 immediately preceding the check valve |1| to the ports 55 in the cylinder bores 53, thereby admitting or discharging fluid to and from the space to the right of the pistons 52.` An oil line |11 runs by way of a heater (not shown) to the heating chamber 8| of the injector 1|, and to a second line |18 conveying iiuid away from this chamber. Cooling conduits |19 and |80 serve to convey a cooling fluid to and from the cooling passage the entrance to the injection chamber 10.

Running from the tank |6| is an exhaust line |8| leading to the die-clamping valve |52v and not in the reverse to the injector operating valve |82. A line |83 with a manually operated valve |84 serves to interconnect the lines |14 and |8|. From the |82 the lines |85 and |86 run to the ports 62 and 51, respectively, on the leftand righthand sides of the injector piston 59. The remaining line |81 runs from the injector operating valve |82 to the line |68 on the opposite side of the check valve |1| from the die-clamping valve |52.

valve General operation In order to start the operation of the machine by clamping the dies 29 and 30 together, the hydraulic pumps |66 and |69 are started in operation, thereby generating fluid pressure which is transmitted to the lines |65 and |68, respectively. The die-clamping is preferably of the piston type, is shifted by the operator so that fluid passes from the line |68, through the check Valve line |5|, where it is augmented by pressure fluid from the leakage pump |66` The fluid continues onward and enters the port |50, proceed- I9 of the booster plunger I14 where it acts against the end of the-internal bore 22 within the main plunger ,-2 f, causing the latter to move rapidly to the right, carrying with it the die carrier |4 and the diev 29.

As the main plunger 2| advances fluid is drawn through the check valve |59 and line |60 from It will be understood, however, that the check valve |59 may be immersed in the tank |6|. This uid is drawn into the space within the cylinder bore to the left of the main plunger 2|, causing this space to be filled with oil. When to a predetermined position, the arm |4a upon the die carrier |4 engages the collar |54c upon the control rod |54, which shifts the valve |54 from its closed position to its open position when the two dies 29 and 30 are almost together. The shifting of the valve |54 admits pressure, through the line |53, the valve |54, the line |55 and-the port |56 to the left-hand end of the main cylinder 20, acting against the end of the main plunger 2| and causing the full force of the plunger to be exerted against the dies 29 and 30. The die assembly continues to move to the right,

pushing the die head |5 and the rods 43 to the valve |52, which |1| and out the the main plunger 2| advances' 90, around against the nome 16, however, because the die head I is now cushioned against the pistons'52 as soon as they are engaged by the enlarged heads 5| of the plungers 43. This engagement takes place slightly before the nozzle 16 is engaged by the socket 40.

Meanwhile, pressure fluid has been flowing through the line |16 to the ports 55 leading into the cylinder bores 53, thereby tending to force the piston heads 52 to the left. In this manner the pistons 52 combine to oppose the pressure exerted by the main plunger 2|. The force exerted by the pistons 52 does not subtract from the total force used to clamp the dies 29 and 30, but merely reduces the force exerted against the end of the nozzle 16. Since the pistons 52 are in the form of piston heads not connected to the plungers 43, the plungers 43 travel rapidly until they engage the piston heads 52, which have been prevented from traveling fully to the left (Figure 5) by the stop-like action of the annular shoulderbetween the cylinder bores 53 and 41. This construction, moreover, permits the use of a small travel of the die 30 which engages the nozzle 16, hence, saves time in closing the dies 29 and 30. Furthermore, this construction minimizes the effect of the fluid displaced by the pistons 52 in speeding up the movement of the main plunger 2|, which naturally occurs when the pistons 52 are moved to the right, because the line |16 leading therefrom is connected to the same pressure line |68 which supplies pressure to move the main plunger 2|. If the movement of the pistons 52 continues for any considerable distance, the main plungeris speeded up to such an extent that the die 3|) strikes the nozzle 16 with a considerably increased velocity. 'I'his shock is minimized by separating the pistons 52 from the plungers 43 and merely giving them mutually contacting engagement. Obviously, a Asavingin the time of closing the dies operates to save time in the opening thereof.

With the dies 29 and 30 now closed and in engagement with the injector nozzle 16, the injector operating valve |82 is shifted to admit pressure from the line |8I, into the line |86 and port 51 leading into the cylinder bore 58 to the right of the piston head 59. This forces the piston 59, piston rod 60 and injection plunger 61 to the left in an injection stroke, thereby filling the dies with plastic material. The electrical control system for the feeding apparatus of the injector operates in the manner previously described, in response to the engagement o'f the limit switches ||5 and ||6 (Figure 6) by the cam 66 on the injection plunger 61.

When the piston 59 first starts to move, it encountersa comparatively low resistance, hence, this causes a drop in pressure in the lines |86 and |81 leading to the line |68. The check valve I1 however, prevents this drop in pressure fromy reaching the line I5 I running to the main plunger 2|, thereby insuring that full pressure is applied for clamping the dies. At this point the leakage pump |66 comes into operation for supplying the small volume of pressure fluid required to take care of any leakage which occurs past the main plunger 2| while the pump |69 is not supplying pressure uid to the main plunger 2|.

After a charge of plastic material has been forced into the cavities of the dies 29 and 30, the injector operating valve |82 is again shifted so that pressure fluid is admitted through the line |85 to the space on the left-hand side of the piston 59, thereby returning the injector plunger 61 to its retracted position. At this point additional material is fed into the injector chamber by the feed screw 99, in accordance with the electrical operation previously described.

After a sufficient time has elapsed for the material to cool in the dies, the die-clamping valve |52 is shifted to its opposite position so that pressure fluid is discharged from the line |68, through the valve |52, the line |12 to the port |13, into the space at the right-hand end of the main cylinder bore 20, returning the main plunger 2| to its starting position and separating the die halves 29 and 30. As the die carrier I4 reaches its retracted position, the knock-out rods 33 and knock-out bar 32 operate -to cause the pins 34 to eject the work-piece from the die.

Meanwhile, the valve |54 has remained open while the main plunger 2| is returned to its retracted position, fluid from the annular chamber 20 being discharged through the port |56, the line |55, the valve |54, the lines |53 and |5I, the valve |52 and the line I8|, into the tank |6I. When the main plunger 2| has reached its fully retracted position, however, the arm |4a on the die carrier I4 engages the second collar |54b, shifting the control rod |54a to the left and closing the valve |54. Valve |84 is normally open and valve |15 is normally closed. During normal operation of the press these valves are not used. When it is desired to get at the nozzley 16 of the injector 1I, however, (Figure 5) the die carriers |4 and l5 are shifted to their open positions, in the manner previously described. The valve |84 is then closed and the valve |15 opened, thereby admitting iiuid from the pump |69, through the line |68, the check valve |1|, the valve |52, the lines |12 and |14 and the manual valve |15 to the cylinder bores 41. This forces the plungers 43 outwardly in the cylinder bores 41, advances the die carrier I5 and uncovers the injector nozzle 16. Before again closing the molds or dies 29 and 30, the valve |15 is closed and the valve |84 opened. Then as the die carrier I4 advances, in the manner previously described, it closes the molds and carries the die carrier I5 back to its normal position.

It will be understood that we desire to cornprehend within our invention such modifications ascome within the scope of the claims and the invention.

Having thus fully described our invention, what we claim as new and desire to secure by Letters Patent, is:

1. In a plastic molding machine, openable and closable die means, a hydraulic plunger connected to said die means for opening and closing said die means, a source of pressure uid connected to said plunger for supplying pressure fluid thereto, a hydraulic cushioning piston, and means for engaging said cushioning piston, said piston-engaging means being connected to said die means and separable during operation from said cushioning piston.

2. In a plastic molding machine, openablel and closable die means, a hydraulic plunger connected to said die means for opening and closing said die means, a source of pressure fluid connected to said plunger for supplying pressure fluid thereto, a hydraulic cushioning piston, means for engaging said cushioning piston, said piston-engaging means being connected to said die means and separable during operation from said cushioning piston, and hydraulic connections between said cushioning piston and said opening and closing plunger.

3. In a plastic molding machine, openable and closable die means, a hydraulic plunger connected to said die means for opening and closing said die means, a source of pressure uid connected to said plunger for supplying pressure iiuid there` to, a hydraulic cushioning piston, and a member engageable with said cushioning piston connected to said die means and movable during operation independently of said -cushioning piston into engagement therewith.

4. In a plastic molding machine, openable and closable die means, a hydraulic plunger connected to said .die means for opening and closing said die means, a source of pressure iluid connected to said plunger for supplying pressure iiuid thereto, a hydraulic cushioning piston, a member engageable with said cushioning piston connected to said die means and movable during operation independently of said cushioning piston into engagement therewith, and hydraulic connections between said cushioning piston and said opening and closing plunger.

5. In a plastic molding machine, openable` and closable die means, a hydraulic plunger connected to said die means for opening and closing said die means, a source of pressure fluid connected to said plunger for supplying pressure fluid thereto, a hydraulic piston rod connected to said die means, and a cushioning piston movable independently of said piston rod during one part of the operating cycle of the machine and engageable by said piston rod and movable therewith during another part of said operating cycle.

6. In aplastic molding machine, openable and closable die means, a hydraulic plunger connected to said die means for opening and closing said die means, a source of pressure uid connected to said plunger for supplying pressure uid thereto,

a hydraulic piston rod connectedv to said die, a

cushioning piston of different diameter from said piston rod movable independently of and engageable by said piston rod, said piston rod having a vpiston area on the end thereof, and hydraulic cylinders of diierent diameters, said piston rod being mounted in a cylinder of one diameter and said piston being mounted in a cylinder of another .diameter respectively.

7. In a plastic molding machine, openable and closable die means, a hydraulic plunger connected to said die means for opening and closing said die means, a source of pressure fluid connected to said plunger for supplying pressure iiuid thereto, a hydraulic piston rod connected to said die, a cushioning piston of different diameter from said piston rod movable independently of and engageable by said piston rod, said piston rod having. a piston area on the end thereof, and hydraulic cylinders of different diameters, said piston rod being mounted in a cylinder of one diameter and said piston being mounted in a cylinder of another diameter respectively, said cushioning pistonbeing of. greater area than said piston rod.

8. In a plastic molding machine, openable and closable die means, a hydraulic plunger connected to said die means for opening and closing said die means, a source of pressure fluid connected to said plunger for supplying pressure iiuid thereto, a hydraulic piston rod connected to said die, a cushioning piston movable in `alignment with and independently of -said piston rod, said piston rod having a piston area thereon engageable with one side of said cushioning piston, and means for supplying pressure uid selectively to both sides of said cushioning piston, whereby to move said cushioning piston and said piston rod as alunit during one part of the operating cycle of said machine and independently of one another during another part of said operating cycle.

9. In a plastic molding machine, openable and closable die means, a hydraulic plunger connected to said die means for opening and closing said die means, a source of pressure fluid connected to said plunger for supplying pressure uid thereto, a hydraulic piston rod connected to said die, a cushioning piston separable from said piston ro'd and movable independently thereof but engageable by said piston rod, said piston rod having a piston area thereon, said piston area being smaller than the area of said cushioningpiston,

and means for supplying'pressure fluid to said' piston rod area whereby to move said piston rod I having a piston area thereon smaller than the area of said cushioning piston and opening into a separate chamber, and means for supplying pressure fluid to said piston rod areawhereby to move said piston rod independently of said cushioning piston.

WALTER ERNST. IRA B. LAWYER. 

